The present invention relates to a tablet sampler assembly of the kind that may be used to extract tablet samples from a tablet coating machine.
Tablet coating machines are used in the pharmaceutical industry to apply a coating to medicament tablets. For instance, tablets with an unpleasant taste may be coated with a sweet-tasting coating, such as a sucrose-based coating, so as to make them more palatable and thus more comfortable to swallow. As another example, tablets may be coated with a substance containing an active drug in order to target the release of the active pharmaceutical ingredient in, for example, the lower intestinal tract. Conventional coating machines comprise a circular drum defined by a circumferential peripheral wall and two frustoconical end walls. One or both of these end walls have apertures through which the drum can be loaded or unloaded. The drum is filled with a bed of tablets to be coated, and then rotated about its axis. As the drum rotates, the coating material is applied (commonly being sprayed from one or more spray guns positioned within the drum). Rotation of the drum agitates and mixes the bed of tablets, thereby evenly distributing the coating material into a layer which encompasses each of the tablets.
The peripheral wall of the drum is often porous (for instance being semi-perforated or fully perforated). In such cases the drum is often located within a housing to which warm air is supplied, and an open face of a plenum (also known as a suction shoe) is mounted in the housing at the point where the tablet bed lies while the drum is rotating. As the drum rotates, suction from the plenum sequentially draws warm air into the drum from the housing (through the porous peripheral wall of the drum), and from the drum through the tablet bed. Warm air passing through the tablet bed dries the coating on each of the tablets.
It is desirable to take samples of the tablet bed at one or more selected intervals during the coating process, for instance to inspect the evenness of the coating and the thickness of the coating layer. However, it is important that the drum rotates continuously throughout the coating process so that the tablet bed is continuously mixed, ensuring an even coat and preventing the coating material from sticking the tablets to one another. Sampling must therefore take place whilst the drum is in motion. Conventionally, sampling is performed by an operator reaching into the drum as it rotates and scooping out the required quantity of tablets. Such a practice is, however, inherently dangerous, particularly since coating machines often have drums with mixing baffles to assist with agitation of the tablet bed, and/or unloading blades to assist with emptying of the drum after the coating process is complete, and these can impact or trap body parts or clothing, potentially leading to operator injury.
One known coating machine addresses this problem by including a hose which projects into the drum and allows a sample from the tablet bed to be removed by suction through the hose due to the negative vacuum pressure applied. Though such a proposition may reduce the risk of operator injury, the generation of the vacuum pressure is and noisy, and adds additional bulk to the machine. In addition, in many pharmaceutical coating operations it is imperative that there is no opportunity for egress of coating material or tablet matter (such as dust given off by the tablet bed). The air with which the tablets are suctioned through the hose must therefore be filtered, further increasing the complexity and bulk of the machine. Furthermore, the hose obstructs the flow of warm air, the movement of the tablet bed and the spray of coating material from the spray guns, adversely affecting the evenness of the coating. Tablets may also collide with the pipe with sufficient force to break them.